Reducing exhaust backpressure increases airflow velocity and performance. Reducing restrictions using headers, larger size exhaust tubing, shorter length, and installing high-flow catalytic converters and mufflers decrease backpressure.

For street use, large tubing removes energy from the exhaust by slowing exhaust gas velocity; essential in creating a vacuum behind the closed exhaust valve and cooling the gases. Exhaust gasses may be 1500 degrees or more at the port but only 150 degrees at the tailpipe exit. (Turbocharged, NOS engines do not follow this because of pressure differentials).

Reducing backpressure increases exhaust scavenging from the combustion chamber reduces mixture contamination and increase high-end horsepower at the cost of low-end torque by an equivalent to increasing valve overlap. Increasing backpressure is equivalent to decreasing the amount of valve overlap.

Backpressure can be increased by increasing intake velocity since the exhaust stroke must evacuate more air. Increasing intake velocity past the limits of the exhaust system degrades the improvements to the exhaust system.

The total cross-sectional area of tailpipes on an engine should not exceed the total cross-sectional area of primary header pipes (including race engines). The ratios for normal street and highway driving, street performance and street-strip cars are about 45%, 50% and 60%, respectively.